Fabrication and detection technique of fused silica substrate with extremely low subsurface damage

The supersmooth optical substrate with extremely low subsurface damage is essential to obtain high laser damage threshold films. In view of the difference in subsurface morphology, the laser confocal microscope technique combined with light scattering method is firstly used to detect the subsurface defects of fused silica substrates ground by brand W10 and W5 SiC abrasive particles, and the relation between the defects size and the scattering intensity are discussed. Then chemical etching method is introduced to expose the inner features at arbitrary depth for the polished sample, the influences of chemical resultant and redeposition layer on etching rate are analyzed, and the distribution and depth of damage layer are estimated. Furthermore, the relation between RMS roughness and etching